1. Field of the Invention
The invention relates to an applicator for sensors used in the field of medicine.
2. Description of the Related Art
In the field of medicine it is known to insert sensors, especially spiral sensors, into the skin of the patient by rotation, i.e., to screw a spiral sensor with its usually very sharp front end into the skin of the patient in a spiral type motion consisting of application-pressure and torque.
This is the case for example with the wide-spread fetal scalp electrodes which are used to anchor a sensor in the scalp of an unborn child in order to measure the ECG of the unborn child after membranes are ruptured.
Optical sensors can be housed in the tip of such spiral sensors, too, for example for fetal pulse oximetry, with the help of which a direct monitoring of the oxygen saturation in the blood of the unborn child can be established.
Such a sensor is disclosed in the DE-C 3810 008. C1
Since the spiral sensors are applied at a location which is out of view, that is to say behind the vagina of the mother within the uterus, it is a problem for the user to apply these spiral sensors with the correct amount of torque. If too much of a torque is applied, injuries of the fetal scalp are possible as well as a damage of the sensor and the applicator respectively or the perfusion at the site of the application can be restricted by too high an axial pressure of the sensor relative to the patient.
If too small of a torque is applied, the sensor is only poorly anchored in the skin of the patient and it comes loose due to the dynamic stresses occurring during the delivery and the vaginal examinations during the delivery respectively. Moreover too weak an application results in distortions of the signals derived from the sensor.
The application of the correct torque gets even more difficult because the sensor is located at the front end of a thin, long plastic rod or plastic tube respectively and because the user is able to turn only the rear end of this rod-like applicator. With a 20 cm long but just 2 or 3 mm thick rod the bending and the torsion of this rod-like applicator limits the user's feeling for the correct torque.
It is therefor the object of the present invention to provide an applicator which limits the torque during the insertion of the sensor into the tissue of the patient at least in respect to a maximal torque on the one hand, but on the other hand guarantees a necessary minimal torque during the application as well.
Thus the minimal torque guaranteed by the torque limiter may coincide with maximal torque to form a threshold value, that is to say, the very threshold value at which the torque limiter slips.